In the art of making ophthalmic lenses, it is necessary to form the lens to the desired optical power and to fit the lens to the glasses frame.
In the past to establish the optical power, the optical surfaces of the lens may have been rough cut or ground by use of generator tool, sometimes also called a generator ring or bell, and then, subsequently first fine finished, second fine finished, and finally polished to a translucent smooth surface finish using abrasive pads, such as shown in U.S. Pat. Nos. 3,225,497 and 3,522,680. Both glass and plastic lens optical surfaces have been machine finished to translucent finishes using the above or similar techniques. Generally, the initial grinding to form the optical surface took about twenty to thirty seconds, the first fine finish took about two minutes, the second fine finish took about two minutes, and the final polishing took about four to six minutes, giving a total time of about 81/2 to 101/2 minutes per lens. The above are machine operating times and do not include the time to mount and demount the lens. Usually, the generator ring machine was used for grinding; similar or other machines could be used for each of the two fine finishes; and abrasive pads were used for polishing the optical surfaces of the lens. Thus, it was necessary to set-up the lens four times, once on each machine. This resulted in additional time, effort and expense. While generator tools have been used to cut and first and second fine finish lenses, heretofore, it is not believed generator tools or rings have been capable of and/or used to final polish the optical surfaces of the lens to a translucent finish. That is because, heretofore, generator tools or rings were relatively coarse and not capable of providing a smooth translucent polished finish.
That prior art generator tools were not, heretofore, used for polishing is born out by the fact that many of the generator machines now is use are not sufficiently rigid and or close toleranced enough to carry out a polishing operation.
After the optic power of the lens is established, the edges of the lens are ground to fit the selected frame. For example, see U.S. Pat. Nos. 3,673,738; 4,176,498; 4,233,784 and 4,286,415, which patents are incorporated herein by reference. In these patents, the lens whose edge is to be ground is mounted between a pair of blocks which are rotated by a motor. The edge of the lens is engaged first with a generally flat grinding wheel to bring it to the overall desired size, and then the lens is engaged with a second wheel which can have various retaining shapes, such as a bevel. The second wheel may have, for example, a V-shaped groove formed therein and causes a complimentary raised groove to form on the lens suitable for mounting the lens in similar groove on the frame. The shaped edge of the lens is then polished to a translucent finish.
Generally with glass lenses there has been no problem in polishing the edge as the glass can be machine finished to a smooth, translucent surface with prior art polishing wheels. Even if the entire glass lens is not hidden by the frame, only the relatively smooth, translucent or polished glass is exposed. For example see U.S. Pat. No. 3,710,517 which discloses a process for finish polishing glass lenses using a lap material made from diamond particles of an average diameter of 12 microns (8 to 16 microns being preferred) in a an epoxy binder which can be molded to various forms.
Polishing the edges of plastic lenses (such as polycarbonate plastic) to a translucent finish, still presented a problem. Plastic ophthalmic lenses, of course, have come into widespread use because they are lighter in weight than glass, and thus, cause the wearer less discomfort, if worn for a long period of time. However, heretofore, one of the disadvantages of plastic ophthalmic lenses has been that when machine ground to size and machine shaped or beveled on equipment, like that discussed above, the edges of the lens were not completely translucent, but had an opaque or frosted appearance. While the opaque edge was not a problem where the lens edges were completely hidden by the frame, it was a problem in certain powers and certain type or style frames. In higher power optic lenses, generally, at least a portion of the lens edge was exposed no matter what the frame style chosen. In half, partial or rimless frames, again, at least a portion of the lens edge was exposed. In these situations, it was particularly desirable for appearance sake to provide a translucent and not merely opaque or frosted surface on the edge.
While the optical surfaces of plastic lenses have been machine lapped to a translucent finish, this technique could no be used on lens edges as they are not as uniform as the optical surface, the edges being in different shapes to conform to various style frames. Heretofore, it was impossible to polish the edges of plastic lenses on the same machine used to grind and bevel the edges of the plastic lens. Instead, the plastic lens had to be removed from the edging machine and manually polished, using, for example, a buffing wheel and buffing compound. This of course resulted in increased time, labor and cost in manufacture of the finished lens. Further, the time to manually polish the lens was considerably longer than if a machine operation was possible. Heretofore, such machine operation was not possible because the polishing wheels previously used on such edging equipment were not capable of providing the desired smooth translucent surface to the plastic lenses, but instead tended to chip or otherwise mar or scratch the plastic. At best, while somewhat smooth, the plastic edge was still opaque or frosted in appearance.